Caulking apparatus

ABSTRACT

During a caulking process, a pressure is applied to a pressure receiving shoulder portion in the same direction as a direction of a clamping force generated by a caulking portion. The clamping force for holding an outer race can thereby be increased. Also, a pressure receiving surface of the pressure receiving shoulder portion is set higher than an end face. Thus, no pressure resulting from plastic deformation in a direction perpendicular to the direction of the clamping force of the caulking portion is generated. In addition, a groove is formed between the pressure receiving shoulder portion and an end serving as the caulking portion.

INCORPORATION BY REFERENCE

This is a divisional application of U.S. patent application Ser. No.12/697,489, filed on Feb. 1, 2010, claiming priority based on JapanesePatent Application No. 2009-061488 filed on Mar. 13, 2009, thedisclosures of which, including the specification, drawings and abstractis incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a caulked retaining member, one end of which isbent through a calking process to form a caulked portion, that holds amember along a base of the caulked retaining member through the clampingforce of the caulked portion, a method for retaining a member bycaulking, a structure of a caulked retaining member, and a caulkingapparatus for a caulking process.

2. Description of the Related Art

There is known a rotation-translation conversion actuator that ismounted in an internal combustion engine or the like to apply atranslational driving force to the engine (e.g., see Japanese PatentApplication Publication No. 2007-303408 (JP-A-2007-303408) and JapanesePatent Application Publication No. 2007-303479 (JP-A-2007-303479)). Thepublications, JP-A-2007-303408 and JP-A-2007-303479 each describe arotation-translation conversion actuator that drives a valve lift deviceof an internal combustion engine. A rotary body is rotatably supportedin the main body case of the rotation-translation conversion actuatorvia a bearing. The rotary body is rotationally driven by a motor. Thus,a screw shaft makes a translational movement in an axial direction todrive the valve lift device.

In JP-A-2007-303408 and JP-A-2007-303479, an annular support member isarranged inside the housing and bolted to an inner surface of thehousing to fix the bearing for rotatably supporting the rotary body inthe housing.

However, due to the configuration in which the annular support member isarranged inside the housing and fastened by the bolt to fix the bearingas described above, the housing tends to be large. In order to preventthe housing from increasing in size, a method of supporting the bearingthrough a caulking process instead of using the annular support memberor bolting the annular support member.

However, if the housing is simply caulked and the bearing is clamped inthe housing in the case where a member requiring a certain clampingforce, such as the bearing or the like, is held by the housing, theresidual axial force of the housing as a force serving to generate theclamping force cannot be sufficiently increased. As a result, theclamping force for holding the bearing may become insufficient. In orderto increase the residual axial force, it is conceivable to apply apressure to a base of a work in the same direction as the direction ofthe clamping force apart from a position where the work is bent throughthe caulking process.

However, in the caulking process for the bearing as described above, therotational resistance of the bearing needs to be held small. For thispurpose, the application of the pressure for increasing the residualaxial force needs to be prevented from increasing in the radial strainof the bearing.

As a caulking process for other purposes, there are known an art inwhich the inflexion point of a change rate of a pressure exerted by anelectric press is set as a completion point of the press operation (seeJapanese Patent Application Publication No. 2001-162396(JP-A-2001-162396)) and an art in which an inflexion point correspondingto a decrease in the caulking load of a caulking punch is detected basedon the relationship between the caulking load and a caulking stroke ofthe caulking punch to control the amount of a material with which agroove is filled (see Japanese Patent Application Publication No.2002-35864 (JP-A-2002-35864)).

In addition, conventionally a groove is formed between a caulkingportion of a workpiece and a contour region of the workpiece to preventa caulking process from affecting the contour of the work (see JapanesePatent Application Publication No. 2005-34857 (JP-A-2005-34857)).Further, there are known an art in which a load is applied to a bearingside to increase the clamping force resulting from caulking (seeJapanese Patent Application Publication No. 2008-223840(JP-A-2008-223840)), and an art in which a spherical bearing is fixed toa housing by tumbling one of both sides separated from each other by aV-shaped groove (see Japanese Patent Application Publication No.2002-21867 (JP-A-2002-21867)).

If a configuration is adopted in which a held member, such as a bearingor the like, is held by a caulked portion by applying pressure to thebase of a workpiece in the same direction as the direction of a clampingforce without applying pressure to the caulking portion, it isconceivable to further combine with this caulking process the method inwhich the inflexion point of the pressurization force is set as thecompletion point of the press operation as described inJP-A-2001-162396. However, even if this method is combined with thecaulking process, it is unclear whether the member such as the bearingor the like may be restrained from being radially strained as the methoddescribed in JP-A-2001-162396 is put into practice in the caulkingprocess.

This also holds true where the art of the caulking punch described inJP-A-2002-35864 is applied. It is unclear whether the member such as thebearing or the like is restrained from being radially strained throughthe caulking punching.

Furthermore, in JP-A-2005-34857, JP-A-2008-223840, and JP-A-2002-21867,when caulking part of the workpiece onto the member such as the bearingor the like, no consideration is given to the idea of restraining themember from being radially strained.

SUMMARY OF THE INVENTION

The invention restrains a member from being radially strained throughapplication of a pressure to a base of a caulked retaining member in thesame direction as the direction of a clamping force apart from thecaulking portion in a configuration in which a held member is held by acaulked portion.

A first aspect of the invention relates to caulked retaining member thatis bent at one end through a caulking process to form a caulked portionand holds a member along a base of the caulked retaining member by aclamping force of the caulked portion. In the caulked retaining member,the base has a pressure receiving shoulder portion, which receives apressure in a same direction as a direction of the clamping force, andis formed coaxially on the outside of a bent side of the end, and agroove is formed between the end and the pressure receiving shoulderportion.

By using the caulked retaining member that includes the pressurereceiving shoulder portion formed on the base thereof, the pressure canbe applied with the aid of the pressure receiving shoulder portionduring the caulking process of the end. Also, the groove is formedbetween the pressure receiving shoulder portion to which the pressure isthus applied and the end serving as the caulked portion.

Thus, during the caulking process to bend the end, even when thepressure is applied to the pressure receiving shoulder portionsimultaneously and causes deformation, especially plastic deformation,the groove absorbs plastic flow. In this case, the groove especiallyabsorbs plastic flow from a member on the pressure receiving shoulderportion side to a member on the end side, that is, plastic flow towardthe member. Accordingly, the caulked portion side can be prevented frombeing radially strained in accordance with deformation of the pressurereceiving shoulder portion after the caulking process.

Thus, in the construction in which the held member is held by thecaulked portion by applying the pressure to the base of the caulkedretaining member in the same direction as the direction of the clampingforce apart from the caulked portion, the member can be restrained frombeing radially strained through application of the pressure.

A second aspect of the invention relates to a caulked retaining memberthat has an end thereof bent through a caulking process to form acaulked portion and holds a member along a base of the caulked retainingmember by a clamping force of this caulked portion. In this caulkedretaining member, the base has a pressure receiving shoulder portion,which receives a pressure in a same direction as a direction of theclamping force, and is formed coaxially on the outside of a bent side ofthe end, and the pressure receiving shoulder portion has a pressurereceiving surface set at such a position that no pressure is applied tothe member as a result of plastic deformation of the caulked portion ina direction perpendicular to a direction of the clamping force.

By using the caulked retaining member having the pressure receivingshoulder portion formed on the base thereof as in the case of theforegoing first aspect of the invention, the pressure can be appliedwith the aid of the pressure receiving shoulder portion during thecaulking process of the end. According to the second aspect of theinvention, the pressure receiving surface of the pressure receivingshoulder portion is set at such a position that no pressure is appliedto the member as a result of plastic deformation of the caulked portionin the direction perpendicular to the direction of the clamping force.

Thus, during the caulking process to bend the end, even when thepressure is applied to the pressure receiving shoulder portionsimultaneously and causes plastic deformation, this plastic deformationallows no pressure to be applied to the member in the directionperpendicular to the direction of the clamping force. Thus, the caulkedportion side can be prevented from being radially strained in accordancewith deformation of the pressure receiving shoulder portion after thecaulking process.

Thus, in the construction in which the member is held by the caulkedportion by applying the pressure to the base of the work in the samedirection as the direction of the clamping force apart from the caulkingportion, the held member can be restrained from being radially strainedthrough application of the pressure.

A third aspect of the invention relates to a method for retaining amember by caulking. This method includes bending an end of a caulkedretaining member along a corner portion of the member by a caulkingsurface of a caulking roller and the member is held along a base of thework by a clamping force of this caulking portion, and applying apressure to the pressure receiving shoulder portion in the samedirection as the direction of the clamping force during this caulkingprocess.

According to the foregoing aspect of the invention, even when plasticdeformation results from the pressure applied to the pressure receivingshoulder portion in the same direction as the direction of the clampingforce through the caulking process of the above-described caulkedretaining member by the caulking roller during this caulking process,the caulked portion side can be prevented from being radially strainedin accordance with deformation of the pressure receiving shoulderportion after the caulking process, and the member can be restrainedfrom being radially strained.

A fourth aspect of the invention relates to a method for retaining amember by caulking. The method includes: bending an end of a workpiecealong a corner portion of the member by a caulking surface of a caulkingroller; applying a pressure to a pressure receiving shoulder portion,which is formed coaxially on the outside of a bent side of the end ofthe workpiece, in a same direction as a caulking pressure applied to thecaulking surface so that a caulking process is performed to form acaulked portion, and the member is held along a base of the workpiece bya clamping force of the caulked portion; and setting a timing forstarting a caulking end process to a timing when a caulking load appliedto the caulking roller during the caulking process or a caulking torquefor rolling the caulking roller undergoes a specific change indicatingthat the member begins to be strained.

By setting as the timing for starting the caulking process endprocessing the timing when the caulking load or the caulking torqueundergoes a specific change indicating that the member begins to bestrained as described above, the caulking process can be ended prior toan increase in the amount of plastic deformation resulting fromapplication of a pressure to the pressure receiving shoulder portioneven when the pressure is applied to the pressure receiving shoulderportion during the bending of the end through the caulking process.

Thus, the caulked portion side can be prevented from being strained inthe direction of the member in accordance with plastic deformation ofthe pressure receiving shoulder portion after the caulking process.Thus, in the construction in which the member is held by the caulkedportion by applying the pressure to the base of the caulked retainingmember in the same direction as the direction of the clamping forceapart from the caulked portion, the held member can be restrained frombeing radially strained through application of the pressure.

A fifth aspect of the invention relates to a caulking apparatus thatbends an end of a workpiece along a corner portion of a member by acaulking surface of a caulking roller, applies a pressure to a pressurereceiving shoulder portion, which is formed opposite a bent side of theend, in a same direction as a caulking pressure applied to the caulkingsurface to thereby carry out a caulking process and hence form a caulkedportion, and carries out a caulking process of holding the member alonga base of the workpiece by a clamping force of the caulked portion. Thecaulking apparatus is equipped with a workpiece mount, a rollingpressurization unit that presses the workpiece arranged on the workpiecemount as the caulking roller is rolled over the workpiece, a caulkingprocess load state detection unit that detects a caulking process loadapplied by the caulking roller, a specific change detection unit thatdetects a specific change in the caulking process load detected by thecaulking process load state detection unit that indicates the heldmember begins to be strained, and a caulking process changing unit thatchanges a caulking process for the workpiece on a basis of a timing atwhich the specific change detection unit detects the specific change.

When the specific change detection unit detects that the caulkingprocess load state undergoes a specific change indicating that themember begins to be strained during the caulking process by the rollingpressurization unit, the caulking process changing unit changes thecaulking process for the workpiece on the basis of the timing when anoccurrence of this specific change is detected.

The caulking process is changed by, for example, reducing the pressurefor the caulking process or stopping the caulking process itself. Thus,the amount of plastic deformation can be prevented from increasingthrough application of a pressure to the pressure receiving shoulderportion.

Thus, in the caulking apparatus that applies a pressure to the base ofthe workpiece in the same direction as the direction of the clampingforce apart from the caulked portion to hold the member by the caulkedportion, the member can be restrained from being radially strainedthrough application of the pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a longitudinal sectional view of a rotation-translationconversion actuator according to the first embodiment of the invention;

FIG. 2 is a partially cutaway perspective view of a planetarydifferential screw type rotation-translation converter employed in therotation-translation conversion actuator;

FIG. 3 is a longitudinal sectional view showing an assembledrotation-translation conversion actuator according to the firstembodiment of the invention, before caulking;

FIG. 4 is a sectional view showing the shape of the tip portion of abearing holder according to the first embodiment of the invention beforeit is caulked;

FIG. 5 is an explanatory view of the arrangement of a caulking rollerand the bearing holder according to the first embodiment of theinvention;

FIGS. 6A, 6B, 6C, and 6D are explanatory views of the caulking processaccording to the first embodiment of the invention;

FIGS. 7A, 7B, 7C, and 7D are explanatory views of the caulking processaccording to the second embodiment of the invention;

FIG. 8 is an explanatory view of the configuration of a caulkingapparatus according to the third embodiment of the invention;

FIG. 9 is a flowchart of a caulking control process performed by thecaulking apparatus according to the third embodiment of the invention;

FIGS. 10A and 10B illustrate graphs showing how the caulking load andthe caulking torque change with respect to a caulking stroke in thecaulking apparatus according to the third embodiment of the invention;

FIG. 11 is a flowchart of a caulking control process executed by acaulking apparatus according to the fourth embodiment of the invention;and

FIG. 12 is a graph used in a caulking apparatus according to the fifthembodiment of the invention and showing the relationship between acaulking stroke and a bearing strain.

DETAILED DESCRIPTION OF EMBODIMENTS

A longitudinal sectional view of FIG. 1 represents the construction of arotation-translation conversion actuator (hereinafter referred to as“the actuator”) 2 to which the invention is applied. The actuator 2 maybe mounted on an outer surface of a cylinder head or cam carrier of aninternal combustion engine as a driven object device. In particular, theactuator 2 drives a variable valve operating mechanism mounted on acylinder head, and adjusts the axial position of a control shaftinstalled in the variable valve operating mechanism. It should be notedherein that the actuator 2 is mounted on an outer peripheral surface 4 aof a cam carrier 4 as indicated by alternate long and short dash lines.

In a housing 6, constituting a body of the actuator 2, a bearing holder8 is bolted from the front of the actuator housing 6 (on an F side inFIG. 1) and a stator 10 is bolted from the rear of the actuator housing6 (on a B side in FIG. 1). A control panel 12 is bolted to the rear ofthe housing 6. The housing 6 is thereby closed.

Inside the bearing holder 8, a bearing 14 (corresponding to the member)is retained on a rear side of the bearing holder 8 by a caulked portion8 b, which is formed through a caulking process as will be describedlater. The bearing holder 8 rotatably supports, via the bearing 14, anut 16 a that constitutes an outer periphery of a planetary differentialscrew type rotation-translation converter 16.

The planetary differential screw type rotation-translation converter 16is provided in the internal space of the housing 6 along the entireaxial length of the housing 6. As shown in a partially cutawayperspective view of FIG. 2, the planetary differential screw typerotation-translation converter 16 is includes the nut 16 a(corresponding to the rotary member), an output shaft 16 b(corresponding to the sun shaft), and a planetary shaft 16 c arrangedbetween the nut 16 a and the output shaft 16 b. The nut 16 a meshes withthe planetary shaft 16 c. By the same token, the planetary shaft 16 calso meshes with the output shaft 16 b.

As shown in FIG. 1, a rotor 18 is press-fitted to the rear of the nut 16a. The rotor 18 is driven via the stator 10 in response to a drivesignal from the control panel 12, and the nut 16 a thereby rotatesaround its own axis. Due to rotation of this nut 16 a, the planetaryshaft 16 c revolves around the output shaft 16 b while rotating aroundits own axis. A screw differential effect is created through rotation ofthis planetary shaft 16 c around its own axis and revolution around theoutput shaft 16 b. Due to this screw differential effect, the outputshaft 16 b, which is spline-fitted to a tip of the bearing holder 8 toprevent the output shaft 16 b from rotating around its own axis, movesin an axial direction (in an direction of arrows F-B). In accordancewith the movement of this output shaft 16 b in the axial direction, thecontrol shaft of the variable valve operating mechanism located in thespace within the cam carrier 4 moves in the axial direction, and themaximum valve lift amount of an intake valve in each cylinder of theinternal combustion engine may be continuously adjusted through thismovement. Thus, the intake air amount of the internal combustion enginecan be continuously adjusted without using a throttle valve.

As shown in FIG. 1, the bearing 14 supporting the entire planetarydifferential screw type rotation-translation converter 16 includes anouter race 14 a that is sandwiched in the axial direction between anabutment surface 8a formed inside the bearing holder 8 and the caulkedportion 8 b at the rear end. Thus, the entire planetary differentialscrew type rotation-translation converter 16 is held at a predeterminedposition in the housing 6 by the bearing holder 8.

The caulking process for forming the caulked portion 8 b will now bedescribed. FIG. 3 shows a cross-sectional view of an assedmbledrotation-translation conversion actuator before caulking. Beforecaulking, an end 8 x on the rear end of the bearing holder 8(corresponding to the caulked retaining member) assumes a cylindricallyrising shape forms a cylindrical projection. Accordingly, the bearingholder 8 is open on the rear end, and the planetary differential screwtype rotation-translation converter 16 is inserted in the bearing holder8 from the rear of the bearing holder 8. Before insertion, the planetarydifferential screw type rotation-translation converter 16 is fixed by asnap ring 20 with the bearing 14 fitted to the outer periphery of thenut 16 a. In addition, a seal ring 22 is also inserted from the rear endof the bearing holder 8 to be arranged at a predetermined position. Itshould be noted that the seal ring 22 is first fitted to the planetarydifferential screw type rotation-translation converter 16 in advance andthen inserted the insertion of the planetary differential screw typerotation-translation converter 16.

In FIG. 4, a partially enlarged view of the rear end of the bearingholder 8 is shown. In addition to the end 8 x, a pressure receivingshoulder portion 8 y, which receives a pressure in the same direction asthe direction of a clamping force exerted by the caulked portion 8 bshown in FIG. 1 (the form of the end 8 x subjected to the caulkingprocess), is formed on the rear end of a peripheral wall portion 8 c ofthe bearing holder 8 (corresponding to a base of the bearing holder 8)on an outer periphery side of the peripheral wall portion 8 c outside ofthe end 8 x, which is formed on the inner periphery side of theperipheral wall portion 8 c in this case. A groove 8 z with a V-shapedcross-section is formed between the end 8 x and the pressure receivingshoulder portion 8 y.

In bending the end 8 x toward the bearing 14 along a corner portion ofthe bearing 14 through the caulking process, the pressure exerted on thebearing 14 by the caulked portion 8 b (the end 8 x) in the samedirection as the direction of the clamping force is also applied to apressure receiving surface 8 d that is a tip surface of the pressurereceiving shoulder portion 8 y, especially in the final stage of thebending of the end 8 x. The pressure receiving surface 8 d is set higherthan an end surface 14 b of the bearing 14 by a height H.

The configuration shown in FIG. 3 is arranged in a roll caulkingapparatus to subject the end 8 x to a caulking process by two caulkingrollers 24 as shown in FIG. 5. The two caulking rollers 24 are arrangedaround an axis B of the bearing holder 8 at phase intervals of 180°, andare rotated around axes of rotation A respectively. It should be notedin FIG. 5 that the axes of rotation A of the caulking rollers 24 and theaxis B of the bearing holder 8 are shown parallel to the sheet of thedrawing. The axes of rotation A are perpendicular to the axis B.

These caulking rollers 24 have stepless cylindrical outer peripheralsurfaces, a portion of which are used as caulking surfaces 26. Therollers 24 are rotated around their own axes of rotation A respectively,and at the same time, revolve around the axis B of the bearing holder 8.The rollers 24 are thus rolled to press the end 8 x on the caulkingsurfaces 26 formed on the rollers 24 from the state shown in FIG. 6A tothat shown in FIG. 6B, and the end 8 x begins bending toward the innerperiphery side of the bearing holder 8 along the end surface 14 b of theouter race 14 a.

Immediately before the end of the caulking process, the regions 27 ofthe outer peripheral surfaces of the rollers 24 that are adjacent to thecaulking surfaces 26 respectively abut on the pressure receiving surface8 d of the pressure receiving shoulder portion 8 y as shown in FIG. 6C.Thus, a pressure is applied to the pressure receiving shoulder portion 8y from the rollers 24. The pressure is applied in the same direction asthe direction of a clamping force (in the axial direction of the bearingholder 8 in this case) so that the end 8 x is eventually caulked intothe caulked portion 8 b to clamp the bearing 14.

The rollers 24 then press the pressure receiving shoulder portion 8 y tocause plastic deformation while bending the end 8x. Thus, as shown inFIG. 6D, the end 8 x eventually serves as the caulked portion 8 b toclamp the end surface 14 b of the bearing 14, and the caulking processis hence completed.

In the caulking process as described above, the caulking surfaces 26apply pressure to the peripheral wall portion 8 c, which is not to bebent, from the end 8x side in a direction along the axis B (FIG. 5) (inthe direction of the clamping force). However, the regions 27 adjacentto the caulking surfaces 26 press the pressure receiving shoulderportion 8 y as described above, and the pressure is thereby applied tothe peripheral wall portion 8 c in the same direction from the pressurereceiving shoulder portion 8 y as well.

Accordingly, the peripheral wall portion 8 c undergoes elasticdeformation and plastic deformation during deformation of the end 8 xduring the caulking process. The ratio of the amount of plasticdeformation increases due to the pressure from the pressure receivingshoulder portion 8 y, and the amount of elastic deformation decreasescorrespondingly. It should be noted that the outer race 14 a of thebearing 14, which receives a pressure from the end surface 14 b via theend 8 x (which becomes the caulked portion 8 b after the caulkingprocess) during the caulking process, is made of a hard material andundergoes elastic deformation only. For example, although both thebearing holder 8 and the outer race 14 a are made of steels, the steelof the outer race 14 a is harder than the steel of the bearing holder 8.For example, the bearing holder 8 may be made of a conventionalstainless steel or the like, and the outer race 14 a is made of a hardsteel such as high-carbon chrome steel or the like.

Due to a difference between the amount of elastic deformation of theouter race 14 a of this bearing 14 and the amount of elastic deformationof the peripheral wall portion 8 c of the bearing holder 8, a residualaxial force is generated in the bearing holder 8 after the caulkingprocess. Especially due to pressure of the pressure receiving shoulderportion 8 y by the regions 27 adjacent to the caulking surfaces 26 ofthe rollers 24, the amount of plastic flow on the peripheral wallportion 8 c side increases, and the residual axial force therebyincreases. Because the residual axial force thus increased, the outerrace 14 a receives a clamping pressure from the caulked portion 8 bwhile abutting on the abutment surface 8 a, and the entire bearing 14 isreliably held in the bearing holder 8. Thus, the nut 16 a of theplanetary differential screw type rotation-translation converter 16 isrotatably supported in the bearing holder 8.

In the caulking process, plastic deformation resulting from press of thepressure receiving shoulder portion 8 y causes the peripheral wallportion 8 c to bulge toward the inner periphery side as well as towardthe outer periphery side. In this embodiment of the invention, theperipheral wall portion 8 c is prevented from bulging toward this innerperiphery side according to two methods.

In the first method, as shown in FIG. 4, the pressure receiving surface8d of the pressure receiving shoulder portion 8 y is set higher than theend surface 14 b of the outer race 14 a of the bearing 14. Thus, thebulge formed in the peripheral wall portion 8 c, toward the innerperiphery side, due to plastic deformation caused by transmission of apressure toward the inner periphery is absorbed by a range I shown inFIG. 4 so that the pressure does not deform the outer race 14 a of thebearing 14 inward. The range I is obtained by adding a range where theouter race 14 a of the bearing 14 is spaced apart from an inner surfaceof the bearing holder 8 to a range higher than the end surface 14 b ofthe outer race 14 a. In this embodiment of the invention, the range I ishigher than a rounded region R of the corner portion of the outer race14 a.

In the second method, the groove 8 z exists between the end 8 x and thepressure receiving shoulder portion 8 y. Thus, even if the pressure istransmitted to the inner periphery side, most of the plastic deformationresulting from the transmission of the pressure is absorbed by thegroove 8 z.

Thus, pressure of the pressure receiving shoulder portion 8 y does notcause the bearing 14 located in the bearing holder 8 to be strainedradially inward after the caulking process, and does not affect therotational resistance of the nut 16 a of the planetary differentialscrew type rotation-translation converter 16.

According to the first embodiment of the invention in which a method forretaining a member by caulking and a structure of caulked retainingmember are realized with the aid of the caulked retaining member asdescribed above, the following effects are obtained. 1) In subjectingthe end 8 x of the bearing holder 8 to the caulking process, thepressure is applied to the pressure receiving shoulder portion 8 y inthe same direction as the direction of the clamping force generated bythe caulked portion 8 b. Thus, as described above, the residual axialforce in the bearing holder 8 is larger after the completion of thedescribed caulking process than in the case of a conventional caulkingprocess. Thus, the clamping force for holding the outer race 14 a may beincreased.

In addition, the pressure receiving surface 8 d of the pressurereceiving shoulder portion 8 y is set higher than the end surface 14 bof the outer race 14 a. Thus, no pressure results from plasticdeformation of the caulked portion 8 b in the direction perpendicular tothe direction of the clamping force. In addition, the groove 8 z isformed between the pressure receiving shoulder portion 8 y and the end 8x serving as the caulked portion 8 b. Due to these, even when plasticdeformation occurs through application of the pressure to the pressurereceiving shoulder portion 8 y simultaneously with the bending of theend 8 x through the caulking process as described above, plastic flowdoes not affect the bearing 14 side. Thus, the bearing 14 is restrainedfrom being radially strained, namely, from being so strained as toincrease the rotational resistance thereof in accordance withdeformation of the pressure receiving shoulder portion 8 y during thecaulking process.

2) The invention is applied to the caulking process in which the bearing14 for rotatably supporting the planetary differential screw typerotation-translation converter 16 is arranged in the bearing holder 8.Therefore, a large residual axial force may be set for the bearingholder 8, and the bearing 14 may be reliably held while being preventedfrom being radially strained. As a result, the size of the actuator maybe reduced, and energy for driving the actuator can be conserved. Inparticular, because the driven object device is an internal combustionengine, size reduction and energy conservation are made possible for theinternal combustion engine, and fuel economy is improved.

3) The same rollers 24 are used to subject the end 8 x of the bearingholder 8 to the caulking process and apply the pressure to the pressurereceiving shoulder portion 8 y of the bearing holder 8. In addition, therollers 24 are formed as stepless cylindrical surfaces. Thus, thecaulking process may be efficiently carried out using a simpleconfiguration. Furthermore, the shape of the rollers 24 is simplified,so it becomes easy to reduce the cost of the caulking apparatus andincrease the accuracy in caulking the bearing holder 8.

In the second embodiment of the invention, as shown in FIG. 7A, abearing holder 108 has an end 108 x serving as a caulked portion 108 bafter a caulking process, and a pressure receiving shoulder portion 108y having a pressure receiving surface 108 d formed on an outer peripheryside with respect to the end 108 x. However, a groove or the like is notprovided between the end 108 x and the pressure receiving shoulderportion 108 y. The second embodiment of the invention is identical tothe first embodiment of the invention in other structural details.

Using this bearing holder 108, as shown in FIGS. 7B to 7D, the caulkingprocess is carried out with the aid of rollers 124 forming steplesscylindrical outer peripheral surfaces as in the case of the firstembodiment of the invention. In the final stage of the caulking process,a pressure is applied to the pressure receiving surface 108 d of thepressure receiving shoulder portion 108 y as shown in FIGS. 7C and 7D.

In this embodiment of the invention, because no gap is provided betweenthe end 108 x and the pressure receiving shoulder portion 108 y, theeffect of absorbing radially inward plastic flow decreasescorrespondingly. However, because the pressure receiving surface 108 dof the pressure receiving shoulder portion 108 y is set higher than anend surface 114 b of a bearing 114, plastic flow is absorbedcorrespondingly. As a result, an effect of preventing the bearing 114from being radially strained is exerted.

The other effects are the same as described in the first embodiment ofthe invention. In the third embodiment of the invention, a caulkingprocess is carried out using a caulking apparatus 223 shown in FIG. 8.Two caulking rollers 224 are arranged to face each other at phaseintervals of 180° around an axis Ax of a bearing holder 208 arranged ona work mount. The axis of rotation Bx common to the two caulking rollers224 is perpendicular to the axis Ax of the bearing holder 208.

These caulking rollers 224 are lowered along the axis Ax of the bearingholder 208 to bring cylindrical caulking surfaces 228 formed on outerperipheries of the caulking rollers 224 into contact with an end 208 xof the bearing holder 208. The caulking rollers 224 are then rotatedaround the axis Ax of the bearing holder 208 by a rotation mechanism 223a provided in the caulking apparatus 223. Through the rotation of thecaulking rollers, a pressure is applied to rotational shaft bodies 224 aof the caulking rollers 224 from a pressurization mechanism 223 binstalled in the caulking apparatus 223, downward along the axis Ax ofthe bearing holder 208.

The pressurization mechanism 223 b is provided with a pressuregeneration device for generating a hydraulic pressure or the like and apressure adjustment mechanism. The pressure adjustment mechanism appliesa caulking load Fp required for the caulking process to the caulkingrollers 224. This caulking load Fp (N) may be detected by a processmeasurement portion 223 c to be used for an automatic processing by acaulking process control portion 223 d. Furthermore, in the processmeasurement portion 223 c, a caulking stroke Lp (mm), namely, a movingamount of the process rollers 224 in the direction of the axis Ax of thebearing holder 208 is also detected to be output to the caulking processcontrol portion 223 d.

The caulking rollers 224 are supported around the axis Bx rotatablyaround their own axes via the rotational shaft bodies 224 a respectivelyand hence are rotated around their own axes while revolving around theaxis Bx through caulking process. That is, the caulking rollers 224 arerolled.

The shapes of the end 208 x of the bearing holder 208 and the pressurereceiving shoulder portion 208 y of the bearing holder 208 are the sameas shown in the first embodiment or the second embodiment of theinvention. Accordingly, the caulking rollers 224 are brought intocontact with the end 208 x of the bearing holder 208 as described above,then brought into contact with the pressure receiving surface 208 d ofthe pressure receiving shoulder portion 208 y in the final stage of thecaulking process, and rolled, and the caulking process as described inthe first embodiment or the second embodiment of the invention isthereby be carried out.

It should be noted herein that the caulking process control portion 223d is mainly constituted by a microcomputer. A flowchart of FIG. 9 showsa caulking control process executed by the caulking process controlportion 223 d. The proces is executed at predetermined intervals. Itshould be noted that the steps in the flowchart corresponding toindividual processing contents are denoted by “S˜” respectively.

When the present processing is started, it is first determined whetherthe caulking process is being carried out (S102). If the caulkingprocess is not being carried out (NO in S102), the present processing isimmediately terminated. If the caulking apparatus 223 is operated tostart the caulking process, the caulking process is being carried out(YES in S102). Accordingly, the caulking load Fp and the caulking strokeLp, which are detected by the process measurement portion 223 c, arethen read into a working area provided in a transient memory of thecaulking process control portion 223 d (S104).

A caulking load change amount dFp for a last constant stroke changeamount dLp (e.g., a stroke change amount of 0.1 mm) is then calculated(S106). That is, the difference between the caulking load Fp after thecaulking rollers 224 are lowered by a predetermined stroke and thecaulking load Fp before the caulking rollers 224 are lowered iscalculated as the caulking load change amount dFp. The caulking loadchange amount dFp is calculated using formula 1 (S108).

dFp<Adfp+dx   (Formula 1)

The right side of the formula 1 represents a value larger than alater-described caulking load change amount moving average Adfp by adivergence amount dx. That is, the formula 1 is used to determinewhether the caulking load change amount dFp is smaller than the sum ofthe caulking load change amount moving average Adfp and the divergenceamount dx.

More specifically, the caulking load Fp changes as shown in FIG. 10A asthe caulking stroke Lp changes. In FIG. 10A, the caulking process isstarted slightly before the caulking stroke Lp becomes equal to 1 mm.After that, the caulking load Fp rises at a substantially constantgradient shortly after the caulking stroke Lp exceeds 4 mm. The constantchange in the caulking load Fp at a substantially constant gradientarises in the course of bending the end 208 x (8 x, 108 x) as shown inFIGS. 6B and 6C and FIGS. 7B and 7C.

Then, when the rollers 224 (24, 124) press the pressure receivingshoulder portion 208 y (8 y, 108 y) as well to bring the end 208 x (8 x,108 x) into contact with the end surface 214 b (14 b, 114 b) of thebearing 214 (14, 114) as shown in FIGS. 6C and 6D and FIGS. 7C and 7D,the caulking load Fp begins to increase abruptly as indicated by astroke point Lx in FIG. 10A. Accordingly, when the caulking stroke Lpreaches this stroke point Lx, the caulking process is completed.

That is, the formula 1 serves to determine whether the stroke point Lx,where the caulking load Fp begins to increase abruptly, has beenreached. In this case, if the relationship dFp<Adfp+dx is satisfied (YESin S108), the caulking stroke Lp has not reached the stroke point Lx.Accordingly, the caulking load change amount moving average Adfp iscalculated using formula 2 (S110).

Adfp←(n·Adfp+dFp)/(n+1)   (Formula 2)

It should be noted herein that the caulking load change amount movingaverage Adfp on the right side of Formula 2 is a value calculated duringthe previous control cycle (a value used in the last step S108), andthat the caulking load change amount moving average Adfp on the leftside is a currently updated value. The value n representing number oftimes is set to, for example, 10. It should be noted that thecalculation according to formula 2 may be made immediately before stepS108.

The present process is thus terminated. After that, when the caulkingprocess is being carried out and formula 1 continues to be satisfied inthe subsequent caulking control process (YES in S108), the caulking loadchange amount moving average Adfp continues to be calculated accordingto formula 2 (S110).

Then, when the caulking stroke reaches the stroke point Lx, where therelationship dFp≧Adfp+dx is satisfied (NO in S108), a caulking stopprocess is executed (S112). In the caulking stop process, morespecifically, the application of the pressure to the bearing holder 208is stopped by raising the caulking rollers 224, and the caulking rollers224. Furthermore, the rolling of the caulking rollers 224 by therotation mechanism 223 a is stopped.

Due to the execution of the caulking stop process as described above,the caulking process is not being carried out (NO in S102) in thesubsequent caulking control process. Therefore, the present processingis terminated. Further, when the caulking process is next carried out,the result of the determination in step S102 is YES. Then in the processas described above, press and rolling are continued by the caulkingrollers 224 until the caulking process is completed.

In the above configuration, the rotation mechanism 223 a and thepressurization mechanism 223 b are equivalent to the rollingpressurization unit, and the process measurement portion 223 c isequivalent to the caulking process load state detection unit. Thecaulking process control portion 223 d is equivalent to the specificchange detection unit and the process changing unit. Steps S104, S106,S108, and S110 of the caulking control process (FIG. 9) are equivalentto the processes executed by the specific change detection unit, andstep S112 is equivalent to the process executed by the process changingunit.

According to the third embodiment of the invention, the followingeffects are obtained. 1) In accordance with the construction of thebearing holder used for the caulking process, the effects of the firstembodiment or the second embodiment of the invention are obtained.

2) When the end 208 x of the bearing holder 208 is subjected to thecaulking process, the caulking apparatus 223 changes the caulkingprocess for the bearing holder 208 at a timing at which a specificchange occurs that indicates the bearing 214 begins to be strained. Morespecifically, the caulking process is terminated.

Thus, by reducing the pressure for the caulking process or stopping thecaulking process, increases in the amount of plastic deformationresulting from application of the pressure to the pressure receivingshoulder portion 208 y may be prevented.

Accordingly, the caulking apparatus 223 may reliably restrain thebearing 214 from being radially strained as a result of application ofthe pressure in carrying out the caulking process. In the fourthembodiment of the invention, the caulking control process shown in FIG.11 is performed at predetermined intervals. Furthermore, a processmeasurement portion that detects the caulking stroke Lp (mm) and thecaulking torque Tp (N·m) is employed as the process measurement portion223 c. The caulking torque Tp is applied to the bearing holder 208 whenthe caulking rollers 224 rotate around the axis Ax of the bearing holder208 by means of the rotation mechanism 223 a. It should be noted thatthe energy for rotating the rotation mechanism 223 a at a constantspeed, namely, the electric power supplied to an electric motor, may beused as a value indicative of the caulking torque Tp instead ofdetecting the caulking torque Tp using the process measurement portion223 c. The fourth embodiment of the invention is identical to the thirdembodiment of the invention in other structural details. Therefore, thecaulking control process (FIG. 11) will be described with reference toFIGS. 8 and 10.

When the present process is started, it is first determined whether thecaulking process is being carried out (S202). If the caulking process isnot being carried out (NO in S202), the present processing isimmediately terminated. If the caulking apparatus 223 is operated tostart the caulking process (YES in S202), the caulking torque Tp and thecaulking stroke Lp, which are detected by the process measurementportion 223 c, are then stored into the working area of the memory(S204).

A caulking torque change amount dTp for the previous constant strokechange amount dLp (e.g., the stroke change amount of 0.1 mm) is thencalculated (S206). The caulking torque change amount dTp is calculatedusing formula 3 (S208).

dTp>Bdtp−dy   (Formula 3)

The right side of formula 3 represents a value smaller than alater-described caulking torque change amount moving average Bdtp by adivergence amount dy. That is, formula 3 is used to determine whetherthe caulking torque change amount dTp exceeds a value obtained bysubtracting the divergence amount dy from the caulking torque changeamount moving average Bdtp.

More specifically, the caulking torque Tp changes as shown in FIG. 10Bas the caulking stroke Lp changes. In FIG. 10B, the caulking torque Tpchanges without drastically decreasing from the start of the caulkingprocess shortly after the caulking stroke Lp exceeds 4 mm. This arisesin the course of bending the end 208 x (8 x, 108 x) as shown in FIGS. 6Band 6C and FIGS. 7B and 7C.

Then, when the end 208 x (8 x, 108 x) comes into contact with the endsurface 214 b (14 b, 114 b) of the bearing 214 (14, 114) as shown inFIGS. 6C and 6D and FIGS. 7C and 7D, the caulking torque Tp startsabruptly decreasing as indicated by a stroke point Ly in FIG. 10B. Thisindicates that the bending of the end 208 x of the bearing holder 208and plastic deformation of the pressure receiving shoulder portion 208 yare terminated to cause a decrease in the resistance against the rollingof the caulking rollers 224. Accordingly, when the caulking stroke Lpreaches this stroke point Ly, the caulking process is completed.

That is, formula 3 is used to determine whether the caulking stroke Lphas reached the stroke point Ly, where the caulking torque Tp begins todecrease abruptly. The stroke position is substantially the same as thestroke point Lx, as shown in FIG. 10A.

In this case, if the relationship dTp>Bdtp−dy is satisfied (YES inS208), the caulking stroke Lp has not reached the stroke point Ly.Accordingly, the caulking torque change amount moving average Bdtp isthen calculated using formula 4 (S210).

BdTp←(m·Bdtp+dTp)/(m+1)   (Formula 4)

It should be noted herein that the caulking torque change amount movingaverage Bdtp on the right side is a value calculated during the previouscontrol cycle (a value used in a step S208 executed previously), andthat the caulking torque change amount moving average Bdtp on the leftside is the current value. A value m representing number of times is setto, for example, 10. It should be noted that the calculation accordingto formula 4 may be made immediately before step S208.

After that, when the caulking process is being carried out and formula 3continues to be satisfied (YES in S208), the caulking torque changeamount moving average Bdtp continues to be calculated according toformula 4 (S210).

Then, when the caulking stroke Lp reaches the stroke point Ly where therelationship dTp≦Bdtp−dy is satisfied (NO in S208), the caulking stopprocess is executed (S212). The caulking stop process is the same asthat described in step S112 of the third embodiment of the invention.

In the above configuration, steps S204, S206, S208, and S210 of thecaulking control process (FIG. 11) are equivalent to the processesexecuted by the specific change detection unit, and step S212 isequivalent to the process executed by the process changing unit.

As described above, in this embodiment of the invention, thedetermination of whether to stop the caulking process is based on thecaulking torque change amount dTp. The effects described in the thirdembodiment of the invention are obtained from this as well.

In the fifth embodiment of the invention, the caulking stop process(S112, S212) executed in the caulking control process (FIGS. 9 and 11)differs in that the caulking process continues for a brief period beforethe caulking stop process is executed as described above.

That is, as shown in FIG. 12, when the caulking process progressesbeyond the stroke point Lx, Ly (the origin in FIG. 12), the strain ofthe bearing 214 is caused and increased as the caulking stroke Lpincreases. If the strain of the bearing 214 is within a permissiblerange, it is preferable, in view of various errors during the process,to stop the caulking process after the caulking stroke Lp slightlyexceeds the stroke point Lx, Ly, so that the bearing 214 is held with asufficient clamping force.

For example, if the permissible range of the strain of the bearing 214is equal to or smaller than 5 μm, it was experimentally determined thatthe caulking stroke Lp may exceed the stroke point Lx or Ly by 0.2 mm.Accordingly, a shift to the caulking stop process (S112, S212) is madeafter the caulking stroke Lp exceeds the stroke point Lx, Ly by a valuesmaller than 0.2 mm, for example, 0.1 mm.

Thus, the effects of the third embodiment of the invention or fourthembodiment of the invention are achieved, and the caulking process maybe reliably carried out in view of various errors during the caulkingprocess. Modified examples will be described hereinafter. (a) In eachdescribed embodiment of the invention, the caulking apparatus includestwo caulking rollers arranged around the axis of the bearing holder atphase intervals of 180°. However, the caulking apparatus may have onlyone caulking roller. Alternatively, a caulking apparatus having threecaulking rollers arranged at phase intervals of 120° or a caulkingapparatus having four caulking rollers arranged at phase intervals of90° may be employed.

(b) In each of the described embodiments, the outer race of the bearingis clamped by the bearing holder. However, it is also appropriate toadopt a structure in which the caulked portion is formed directly on thehousing through a caulking process and the outer race of the bearing isdirectly held by the housing instead of using the bearing holder. Inthis case as well, an effect similar to that of the case where thepressure receiving shoulder portion is formed on the housing and held bythe bearing holder as described above through application of thepressure is obtained.

In each embodiment of the invention, the pressure receiving shoulderportion is described as being formed on the bearing holder or thehousing for the purpose of application of the pressure. However, if thebearing holder or the housing already has a region to which a pressuremay be applied in the direction of the clamping force of the outer race,that region may be utilized as the pressure receiving shoulder portioninstead.

Further, the pressure receiving shoulder portion is pressed by the samerollers as the caulking rollers for subjecting the end to the caulkingprocess. However, the pressure receiving shoulder portion may be pressedby a different type of pressurization mechanism. Even if the samecaulking rollers as described above are used, the rollers may have acaulking surface and a pressurization surface that are different inlevel from each other instead of having a stepless cylindrical surface.

(d) In each of the above-described caulking control processes, thecaulking load change amount moving average Adfp (FIG. 9: S110) or thecaulking torque change amount moving average Bdtp (FIG. 11: S210) iscalculated, and the caulking process stop process is started when thedifference between the latest caulking load Fp or the latest caulkingtorque Tp and the moving average value exceeds the divergence amount dxor dy. Instead of calculating the moving average value and making adetermination as described above, it is also appropriate to provide afilter circuit to filter a signal output from the process measurementportion 223 c and make a determination on a sudden change in thecaulking load Fp or the caulking torque Tp in accordance with thefiltered signal.

(e) In each of the foregoing embodiments of the invention, the variablevalve operating mechanism that adjusts the maximum valve lift amount ofeach intake valve provided in the internal combustion engine is employedas the mechanism driven by the rotation-translation conversion actuator.However, a variable valve operating mechanism capable of continuouslyadjusting the maximum valve lift amount of each exhaust valve providedin the internal combustion engine may be employed instead. Furthermore,a mechanism other than the variable valve operating mechanism may beemployed as the mechanism driven by the rotation-translation conversionactuator. Further, this mechanism may not necessarily be used for theinternal combustion engines.

(f) In each of the described embodiments of the invention, the planetarydifferential screw type rotation-translation converter is adopted as therotation-translation converter. However, a different type ofrotation-translation converter such as a feed screw mechanism may beemployed.

(g) As described in FIG. 4 of the first embodiment of the invention, thestrain toward the outer race 14 a side of the bearing 14, which iscaused through pressurization of the pressure receiving surface 8 d, isabsorbed by the range I including the rounded region R of the cornerportion of the outer race 14 a. Accordingly, the creation of a strainleading to an increase in the rotation resistance of the bearing 14 canalso be suppressed by setting the height of the pressure receivingsurface 8 d higher than a lowest position of this rounded region R.

What is claimed is:
 1. A caulking apparatus that bends an end of aworkpiece along a corner portion of a member by a caulking surface of acaulking roller, applies a pressure to a pressure receiving shoulderportion, which is formed opposite a bent side of the end, in a samedirection as a caulking pressure applied to the caulking surface tothereby carry out a caulking process and hence form a caulked portion,and carries out a caulking process of holding the held member along abase of the workpiece by a clamping force of the caulked portion, thecaulking apparatus comprising: a workpiece mount; a rollingpressurization unit that presses the workpiece arranged on the workpiecemount as the caulking roller is rolled over the workpiece; a caulkingprocess load state detection unit that detects a caulking process loadapplied by the caulking roller; a specific change detection unit thatdetects a specific change in the caulking process load detected by thecaulking process load state detection unit that indicates the memberbegins to be strained; and a caulking process changing unit that changesa caulking process for the workpiece based on a timing at which thespecific change detection unit detects the specific change.
 2. Thecaulking apparatus according to claim 1, wherein the caulking processchanging unit starts a caulking termination process to change thecaulking process.
 3. The caulking apparatus according to claim 1,wherein the caulking process load state detection unit detects a changein a caulking load with respect to a moving distance of the caulkingroller as a caulking process load created by the caulking roller.
 4. Thecaulking apparatus according to claim 3, wherein the specific changedetection unit detects a state of an abrupt increase in the caulkingload as a state of an occurrence of a specific change indicating thatthe member begins to be strained.
 5. The caulking apparatus according toclaim 1, wherein the caulking process load state detection unit detectsa change in a caulking torque with respect to a moving distance of thecaulking roller as a caulking process load created by the caulkingroller.
 6. The caulking apparatus according to claim 5, wherein thespecific change detection unit detects an abrupt decrease in thecaulking torque as a specific change indicating that the member beginsto be strained.
 7. The caulking apparatus according to claim 1, wherein:the member is a bearing; and the workpiece is a housing thataccommodates a rotary member rotatably supported by the bearing, or abearing holder arranged in the housing.
 8. The caulking apparatusaccording to claim 7, further comprising: a rotation-translationconversion actuator, wherein: the bearing and the housing or the bearingholder are a bearing and a housing or a bearing holder of therotation-translation conversion actuator respectively; the housing ismounted on a driven object device; and the rotation-translationconversion actuator includes an output shaft, which moves in an axialdirection of the workpiece through rotation of the rotary member, andprotrudes outward from the housing to transmit a driving force from theoutput shaft to the driven object device.
 9. The caulking apparatusaccording to claim 8, wherein: the rotary member is a nut of a planetarydifferential screw type rotation-translation converter; the output shaftis a sun shaft; a planetary shaft is arranged between the nut and thesun shaft; and the sun shaft and the planetary shaft mesh with the nutin a manner to perform rotation-translation conversion.
 10. The caulkingapparatus according to claim 8, wherein the driven object device is aninternal combustion engine.